Quality control method

ABSTRACT

A method of quality control to diagnose the cause of a malfunction of an instrument. The method uses measurements of the physical property of a sample to diagnose the cause of a malfunction of an instrument. The spatial position of a control product sample is analyzed. Alternatively, the spatial position of a statistically significant number of patient blood samples can be used. The method enables the monitoring of an instrument for problems associated with debris and noise caused by red cell lysis inefficiency; instrument reagents pump volume settings; instrument laser alignments; instrument gain settings; and flow noise caused by partial plugs, residual plugs or other flow problems. The method provides a more specific indication of the type and cause of an instrument malfunctioning than non specific flagging provided by prior art methods.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of application U.S. Ser. No. 08/432,435, filedApr. 28, 1995, now abandoned, which is a continuation-in-part of U.S.Ser. No. 08/386,711 filed Feb. 8, 1995, now U.S. Pat. No. 5,529,933,which is a continuation of Ser. No. 08/081,529, filed Jun. 23, 1993, nowabandoned, which is a continuation of Ser. No. 07/840,438, filed Feb.24, 1992, now abandoned.

FIELD OF INVENTION

This invention relates to a novel method to increase the system qualitycontrol capabilities of hematology instruments. The method hasparticular utility for instruments which measure (1) volume measured byD.C. current, (2) high frequency (RF) size, (3) opacity, and (4) lightscatter to discriminate cell populations of blood. The method has foundadditional utility for instruments which measure (1) volume measured byD.C. current and (2) high frequency (RF) size. The method has also foundutility for instruments that measure cell volume only by D.C. current.

BACKGROUND OF THE INVENTION

Quality control long has been a necessary and routine procedure inclinical hematology. Accuracy in the counting of red blood cells andwhite blood cells, including differentiating among the subpopulations ofwhite blood cells is dependent, in part, upon the use of adequatecontrol products and methods of using the control products. With thenumerous types of equipment for particle counting now available, qualitycontrol by the use of control products is necessary, since thepossibility of malfunctioning of the instrument is ever present. Thetraditional method of maintaining a quality control program forautomatic particle counting equipment has consisted of providing freshhuman blood as a whole blood standard. However, this fresh blood isusable for only one day, therefore, durable blood products weredeveloped.

Hematology control products, which contain reference blood cell analogs,which monitor the accuracy and precision of blood cell counting devicesare important. It is recognized that there is a present need for newmethods of using blood cell analogs for maintaining the accuracy ofwhite cell differentiation and other parameters when employing suchblood cell counting devices.

The control products should approximate that of fresh whole blood asclosely as possible. Attempts have been made to provide suitably sizedparticles in stable suspensions by the use of ragweed pollen,polystyrene, latex, various organic materials and fixed human red cells.None of these suspensions have proved suitable for use as a controlproduct for white cell differentiation of at least four subpopulationsof leukocytes.

The material used for maintaining quality control, hereinafter called ahematology control product or control product, can under specificcircumstances be used also to calibrate hematology instruments. For thepurposes of this invention, the control product used in the method todetermine whether an instrument is properly functioning will contain oneor more analogs suspended in a liquid media, which when analyzedsimulates at least one physical or biological property of blood whichthe instrument is capable of analyzing. As used herein, an analog isdefined as a particle which simulates at least one physical orbiological property of a target population. As such, some automaticmachines are able to analyze only certain components of a controlproduct, despite the control product having additional parametercomponents susceptible to analysis by other machines. Heretofore, therehas been an absence of methods developed for using a control product toprovide quality control of the instrument's performance. Controlproducts typically provide checks for at least four subgroups ofleukocytes namely, lymphocytes, monocytes, neutrophils and eosinophils.Prior art use of control products have focused upon checking whether theinstrument provides the proper count and percentage of the analogs.However, the method of this invention provides additional information toevaluate and diagnose instrument performance.

It is evident that a control product must accurately indicate, on acomparative basis, what a test sample of fresh blood constitutes withregard to the determinations in question. It is further evident howimportant it is for the control product to simulate fresh blood, sinceblood components, such as red blood cells, can hemolyze slowly andundergo changes in size and shape within hours after removal from ablood donor. Similarly, non stabilized white blood cells sufferdegenerative changes.

In general, the process of the prior art for making analogs focused onusing red blood cells which had maintained or reduced their originalvolume prior to fixation. Shrinking or expansion of the cells bymanipulating their osmotic environment prior to fixation has had itslimitations. Previously, shrinking or swelling non-human erythrocytesmore than about 30% to 50% caused excessive cell association or lysis ofthe cell.

U.S. Pat. No. 3,873,467 to Hunt teaches a hematologic reference controlcomprising a suspension of washed, stabilized human red blood cells in anonproteinaceous aqueous suspension fluid that replaces the plasma inhuman blood. Stability in the reference control is attained byconditioning the cells by the inclusion in the aqueous suspension fluidof materials tending to make the cells assume a spherical shape, withoutsubstantial change in the mean cell volume of the cells, as well asimparting to the cells a resistance to the normal tendency of degradingwith time. The aqueous suspension fluid furthermore produces anenvironment for the cells inhibiting biological activity. In a preferredembodiment there is further included in the reference control a minoramount of fixed human red blood cells, processed to have a substantiallyincreased mean cell volume. The fixed cells are resistant to a change incell volume, and to dissolution under the action of lysing reagentsproducing lysing of the stabilized cells. The fixed red blood cells inthe reference control substitute for the white cell population in humanblood.

In U.S. Pat. No. 4,704,364, to Carver, et al., there are disclosedcontrols for thresholds and additional operational performances forelectronic particle counters typified by the COULTER COUNTER® ModelS-Plus type analyzers. However, there is now a need for new methods ofusing a whole blood cell control product for electronic optical particlecounters typified by the COULTER® VCS analyzer. The VCS analyzer permitsthe differentiation of at least four populations of leukocytes.

Any system for automated differential counting of human leukocytes,which distinguishes at least four populations of leukocytes from othercells in the blood on the basis of size range, volume distribution,light scatter range, and electrical opacity and conductivitysensitivities requires that the control product closely simulate therange, distribution and sensitivities characteristics of the respectivecells in normal human blood.

Human lymphocytes, monocytes, neutrophils, basophils and eosinophilshave a specific size distribution range and optical characteristics.Both the upper and lower size limits for each subpopulation ofleukocytes should be represented in a reference control product. Inaddition, the mean cell volume of each leukocyte subpopulation in thecontrol product should approximate that of normal human blood. Moreover,it is necessary that the liquid suspension media used for the controlproduct does not cause significant shrinking or swelling of the cells.Still further, the aging of the control product should not result indeterioration of the volume distribution histogram characteristics orother parameters. A further requirement for the leukocyte analogs in thecontrol product for multi-parameter instruments is that in order to becounted and differentiated, the analog cells in a whole blood controlproduct must not be completely lysed by the lytic reagent.

A variety of media have been used in conjunction with blood cellanalogs. In U.S. Pat. No. 4,299,726, a multi-purpose diluent and a mediais disclosed. The diluent is used to precondition red blood cells andconsists essentially of lactose, sodium azide and a non-ionicsurfactant; is pH adjusted and osmolality adjusted. The media is usedfor a carrier of the whole blood control product and includes lactose,fungicides and antibiotics. It also includes additional components whichalter red blood cell membranes, including bile salts and cholic acidderivatives, phenothiazine compounds and the salts thereof havingantihistamine properties, and 4-amino-benzoic acid ester derivatives andtheir salts having local anesthetic properties.

One disadvantage of the prior art medias is that, when used inconjunction with red blood cells and fixed human white blood cells orwhite blood cell analogs, the control product does not simulate a wholeblood sample in instruments which differentiate at least foursubpopulations of leukocytes. The specific parameters of the red andwhite blood cells which it is desirable to measure dictate some of thenecessary characteristics of a suitable media for a whole bloodreference control product. It is desirable to know the volume of the redcell. Once this measurement is ascertained and the red cells have beencounted, the packed cell volume or hematocrit can be computed.Therefore, the suspension media of the control product should be capableof equilibrating and stabilizing the volume of red blood cells in thesample so that its mean cell volume can be measured (MCV).

A control product should also be rendered free of any particulate matterthat would perhaps demonstrate interference in lower size thresholdscorresponding to that of human platelet size and distribution.Concomitantly, the suspension media would optionally includebacteriostatic agents to prevent the growth of microorganisms afterpackaging the control product.

Although red blood cells (erythrocytes) and white blood cells(leukocytes) nominally have different sizes, their size ranges tend tooverlap, or at least under certain conditions of health could overlap.Moreover, the opacity of these two types of blood cells also mayoverlap. Erythrocytes and the lymphoid leukocytes unfortunately overlapconsiderably in cell sizes, and it is not practical to count one in thepresence of the other by size discrimination alone. Traditional practiceinvolved the use of a strong lytic reagent that stromatolyses theerythrocytes, reducing them to very small particles or causing membranesolubilization, to eliminate them from being counted; and strips most,if not all, of the cytoplasm from the leukocytes, leaving only theirlyse-resistant nuclei to be counted. Since original leukocyte cellvolume is drastically affected and reduced to a minimum, only a singleleukocyte population is discernible by this older form of blood cellsize analysis.

U.S. Pat. No. 3,741,875, Ansley et al., describes a process forobtaining a differential white blood cell count. A cytological fixingagent, which is a monoaldehyde, such as formaldehyde, is added to ablood sample. A hemolyzing agent is added after the fixation step tocause the red blood cells to release their hemoglobin content intosolution. Addition of a specific cytochemical substrate, chromogenicprecipitating coupling reagent, and pH buffer causes deposition of aninsoluble dye in a specific type of cell containing an immobilizedenzyme. The solution containing the dyed blood cells then is passedthrough a photometric counter. Using different specific substrates fordifferent enzymes contained in specific kinds of cells, absolute andrelative counts of the different kinds of cells are obtained. Thecytological fixing solution utilized only a monoaldehyde. Dialdehydesare stated to be unsuitable, since they cross-link and produceextracellular precipitates.

U.S. Pat. No. 4,485,175, to Ledis, et al., concerns a method and reagentsystem for three-volume differential determination of lymphocyte,mononuclear, and granulocyte populations of leukocytes, using quaternaryammonium salts as lysing agents and the COULTER COUNTER® Model S-Plusautomated blood counter, which instrument employs only direct currentfield excitation.

U.S. Pat. No. 4,751,179 to Ledis, et al. describes a reagent system,including saponin in a lysing reagent and a rapidly active cross-linkingagent such as glutaraldehyde as a fixing reagent, which reproduciblyaffects whole blood to cause the red blood cells to stromatolyze andmodifies the leukocytes to generate data to define four distinctclusters for detection and classification by flow analysisinstrumentation. The clusters represent the four major leukocyte typesfound in blood: lymphocytes, monocytes, neutrophils and eosinophils,thus providing a method of leukocyte differential analysis. According toLedis, et al., previous methods of flow analysis of leukocytes usingD.C. volume, or light scatter at various angles have shown only threeclusters of leukocytes, corresponding to lymphocytes, granulocytes andmonocytes. The parameters used by Ledis, et al. for the leukocyteclassification include combinations of two or more of DC (Coulter)volume, high frequency (RF) size, Coulter opacity (RF size/DC volume),light scatter at various angular ranges, and fluorescence at variouswavelengths of illumination.

Electronic counters which employ the Coulter Principle, first describedin U.S. Pat. No. 2,656,508, express a true reflection of particlecounts. According to the Coulter Principle, when a particle ofmicroscopic size is suspended in an electrolyte liquid, is passedthrough an electrical field of small dimensions of an order approachingthose of a particle, there will be a momentary change in the field'selectric impedance. If the electrical field is excited by a direct (DC)or low frequency current, the electrical change is closely proportionalto the volume of the particle. In commercial apparatus, the changes aredetected by some suitable means and used to operate counters andanalyzers. The analyzers associated with such apparatus classify andsize particles into populations based upon particle volume and recordthe data obtained.

The Coulter Principle invention was expanded materially in U.S. Pat. No.3,502,974, Coulter, et al., using radio frequency (RF) current inaddition to DC current field excitation, to provide not only DC volumeinformation concerning the particle studied, but also information due tothe composition and nature of the material constituting the particle.This patent discloses apparatus capable of distinguishing betweenparticles of identical size, but of different material. By generatingthe particle sensing field by means of both a low frequency or directcurrent (DC) and radio frequency (RF) current excitation, two or moreinterrelated output signals can be derived from the passage of a singleparticle through the electrical field. This is due to the fact that,although the particles, such as blood cells, are nearly alwaysinsulators with respect to low frequency or direct current fields, theyare capable of carrying or impeding radio frequency current differentlyfrom the surrounding electrolyte. This may be due to differences in thedielectric constant in the case of homogeneous particles, or to thesac-like structure in the case of blood cells which have, enclosed in anextremely thin membrane, contents having conductivities different fromthe electrolyte. Thus, while all the DC current goes around a bloodcell, some of the RF current will go through it. The ease with which RFcurrent will go through a particle is a measure of what is termed its“electrical transparency”, or simply “transparency”, in analogy withlight transmission; whereas, a particle's ability to impede RF currentis termed its “opacity”. In later publications, “opacity” is defined asthe RF impedance divided by the DC impedance.

The relative electrical opacity of a particle becomes an identifyingfeature of the particle contents and hence its particle type forclassification purposes. To the extent that different types of particleseach possess a different opacity, the difference between them isdetectable. However, significantly different particles can possesssubstantially the same opacity and such particles cannot be classifiedeffectively in this manner. In U.S. Pat. No. 3,836,849, Coulter, et al.taught that it is possible to change selectively the opacity of particletypes by treatment of the particles, so that detectable differencesresult.

The COULTER COUNTER® Model S-Plus automated blood cell counter isdesigned to dilute a sample of whole blood in an isotonic diluent, add alysing agent, and shortly thereafter begin counting. Thus, adiluent-lysing system must provide erythrocyte lysing kineticssufficiently rapid to effect complete stromatolysation of the red bloodcells (erythrocytes) during the lysing period. In addition, changes inleukocyte volume must be minimal during the data collection step, andideally should be stable for several minutes.

COULTER Model VCS is a semi-automated analytical instrument thatanalyzes blood by using DC (Coulter) volume, Coulter opacity and lightscatter at various angular ranges. The COULTER Model VCS uses a reagentsystem to obtain a five part differentiation in the total leukocytecount which provide quantitative analysis of the lymphocyte, monocyte,neutrophil, eosinophil and basophil population. The reagent systemincludes a quench, added after the weak “acid” lyse, the operation ofwhich is to greatly reduce lytic action on the white cells. Shortlyafter the quench, the instrument begins measuring the volume, opacityand light scattering characteristics of the remaining white blood cells.The Model VCS must provide erythrocyte lysing kinetics sufficientlyrapid to effect complete stromatolysation of the red blood cells duringthe lysing period while not affecting the leukocyte cells as to theirvolume, Coulter opacity and light scattering properties. The COULTERCOUNTER® instruments, with which this invention can be used, are theVCs, STKS and MAXM. However, the Model S and S-Plus types are not ableto differentiate all of the subpopulations of leukocyte analogs whichare in a whole blood control product, but rather can provide a totalcount of the leukocyte analogs. Certain of the S-Plus types are furtherable to differentiate two leukocyte subpopulations.

New electronic optical particle counting devices have made it necessaryto develop new methods to determine whether an instrument is properlyfunctioning within manufacturer's specification and diagnosing the causeof an instrument malfunction. Although this Specification will bedirected primarily to method of using hematology control product usefulwith particle counters of the COULTER® type, it should be understoodthat the suspension media, analogs and control products disclosedherein, and their methods of use described herein, find wide applicationwith particle counters generally. Accordingly, the term “electronicoptical particle counter” should be understood to include, in additionto COULTER COUNTER® instruments, any other type of particle counterwhich discriminates between particles of various sizes by the use ofelectronic discriminator circuits (“thresholds”) which respondelectronically to signals indicative of particle size, mass, volume,opacity or light scatter. COULTER and COULTER COUNTER are RegisteredTrademarks of Coulter Corporation.

SUMMARY OF INVENTION

This invention relates to a method for using a hematology controlproduct comprising placing a hematology control product in aninstrument, said control product containing at least one leukocyteanalog which has been derived from a blood cell which has been treatedso that it is resistant to degradation by the lytic reagents used in thehematological test procedures, and the analog remains responsive to thereagents used in the performance of the instrument. The spatial positionof the control product is analyzed from at least one member selectedform the group comprising D.C. volume, RF size, opacity, and lightscatter using new control parameters. More preferably, at least twodifferent physical properties are measured. The results of suchmeasurement are then reported to diagnose the cause of a malfunction ofan instrument.

The invention further relates to a method of using a control productwhich contains at least one leukocyte analog population to determine ifthe instrument is functioning within manufacturer's analyticalspecifications. The method comprises placing a hematology controlproduct in an instrument, said control product containing at least oneleukocyte analog which has been derived from a blood cell which has beentreated so that it is resistant to degradation by the lytic reagentsused in the hematological test procedures, and the analog remainsresponsive to the performance of the instrument. The control productsimulates at least one physical property of a human leukocyte, saidproperty selected from the group comprising volume measured by D.C.current, high frequency (RF) size, opacity, and light scatter. Morepreferably, the control product simulates at least two physicalproperties of a human leukocyte. Then at least one, preferably two ofthe spatial positions from physical properties of the control productare measured. The results of such measurement are reported to diagnosethe cause of a malfunction of an instrument.

Still further, the invention relates to a method comprising analyzingthe spatial position of a leukocyte subpopulation in a quantity ofpatient blood samples to obtain a statistically significant value of ameasured parameter, said analysis selected from at least one member ofthe group comprising D.C. volume, RF size, opacity, and light scatter;and reporting the results of such measurement in an instrument todiagnose the cause of a malfunction of an instrument.

Moreover, this invention also relates to combining a hematologicalsample with a cell suspension media comprising an aqueous solution of aplasma substance; and analyzing the resulting mixture in an instrumentto diagnose the cause of an instrument malfunction, said analysisselected from at least one member and more preferably at least twomembers of the group comprising D.C. volume, RF size, opacity, and lightscatter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a comparison of the COUNT RATIO of the white blood cellscompared to the conductivity of the diluted blood sample in the corethat is to be tested.

FIG. 2 is a comparison of the NEUTROPHIL DC MEAN compared to theosmolality of the blood sample being analyzed after it has been dilutedwith the lytic and quench reagents.

DETAILED DESCRIPTION OF THE INVENTION

For the purposes of understanding and explaining this invention, thefollowing terms are defined.

Beads: Beads are particles (made, usually, of latex or some form ofpolystyrene) that can be used as stable and inert standards for flowcytometric analysis. They can be obtained in different narrowly definedsizes in order to standardize the FSC (standard format for flowcytometric data storage) settings. They can also be obtained conjugatedto various fluorochromes in order to standardize the fluorescencedetection settings.

Channel: Channel is the term by which a flow cytometer characterizes theintensity of the signal emitting by a particle. Most cytometers divideintensity of light signals into 256 for 1024 channels. Signals with highchannel numbers are brighter than signals with low channel numbers;however, the quantitative relationship between signals defined by onechannel number and those defined by another will depend on the amplifierand photodetector voltage characteristic of a given protocol.

Coaxial flow: The flow of a narrow core of liquid within the center of awider stream. Flow of this type is important in flow cytometry becauseit provides a means by which particles flowing through a relatively widenozzle can be tightly confined in space, allowing accurate and stableillumination as they pass one by one through a light beam.

Compensation: Compensation is the ability of a flow cytometer to correctfor the overlap between the fluorescence spectra of differentfluorochromes. Without compensation, fluorescence from a givenfluorochrome may register to some extent on a photodetector assigned tothe detection of a different fluorochrome.

Coulter volume: The increase in electrical resistance that occurs as aparticle displaces electrolyte when it flows through a narrow nozzle isthe particle's Coulter volume. This increase in resistance is onlyroughly related to the volume of the particle.

Core: The core is the stream-within-a-stream that has been injected intothe center of the sheath stream and is maintained there by thehydrodynamic considerations of laminar flow. The core contains thesample particles that are to be analyzed in the flow cytometer.

Cross-talk: Cross-talk is the signal from the “wrong” photodetector thatresults because the fluorescent light emitted by one fluorochromecontains some light of a wavelength that gets through the filters on thephotodetector that is normally specific for the fluorescence from adifferent fluorochrome. See “Compensation.”

CV: The coefficient of variation is defined as the standard deviation ofa series of values divided by the mean of those values. It is used inflow cytometry to describe the width of a histogram peak. Where in someprotocols it can be used to assess the variation in particlecharacteristics within a population. In DNA analysis (where all normalparticles are assumed to have identical characteristics), it isfrequently used to assess the alignment of a flow cytometer (and theskill of the operator).

Fixation: A process by which the protein of cells is denatured. Fixationin flow cytometry is used to inactivate hazardous biological materialand also to preserve stained cells where there is not immediate accessto a flow cytometer. Paraformaldehyde is the fixative of choice for flowcytometry because it preserves the forward and side scattercharacteristics of cells (but causes some increase in theirautofluorescence).

Flow Cell: The flow cell is the device in the flow cytometer thatdelivers the sample stream to the center of the sheath stream. In somecytometric configurations, the illumination occurs “in air” after thestream has left the flow cell.

Fluorochrome: A fluorochrome is a dye that absorbs light and then emitslight of a different color (always of a longer wavelength).

Forward scatter: Forward scatter is light from the illuminating beamthat has been bent (refracted or otherwise deflected) as it passesthrough a particle so as to diverge from the original direction of thebeam. The intensity of the light bent to a small angle from theilluminating beam is related to the refractive index of the particle aswell as to its cross-sectional area. The forward scatter signal is notcorrelated with a cell's volume.

Gain: Gain is the electronic control on an amplifier that determines thecurrent intensity that results when a given signal is received by aphotomultiplier tube. Variation in the gain on photomultiplier tubeamplifiers may vary the appearance of the output signals as they areconverted into flow cytometric data.

Gate: Gate is a restriction placed on the flow cytometric data that willbe included in subsequent analysis. A live gate restricts the data thatwill be accepted by a computer for storage; an analysis gate simplyexcludes certain stored data from a particular analysis procedure. Agate is used to restrict analysis of a mixed population to certain cellswithin that mixed population.

Granularity: Granularity is a term used synonymously with side scatterto describe the light that is deflected to a right angle from theilluminating beam in a flow cytometer. The intensity of this light isrelated, in an imprecise way, to internal or surface irregularities ofthe particles' flow through the beam.

Light scatter: Median angle light scatter (MALS) is defined as thatlight scatter information obtained at angles between 10° and 70°. Lowangle light scatter (LALS) is light scatter information obtained atangles below between 10° relative to the beam axis, excluding 0°. Highangle light scatter (HALS) is light scatter information centered at 90°to the laser axis.

Linear amplifier: A linear amplifier is one means of increasing thesignal from a photomultiplier tube to make it measurable. A linearamplifier increases the signal in such a way that the output currentfrom the amplifier is directly proportional to the input current,derivedfrom the photodetector.

Logarithmic amplifier: Logarithmic amplification is one means ofmodifying the signal from a photomultiplier tube to make it measurable.A logarithmic amplifier modifies the signal is such a way that theoutput current from the amplifier is in proportion to the logarithm ofthe input current derived from the photodetector.

Photodetector: A photodetector is a device that senses light andconverts the energy from that light into an electrical signal. Withinthe operating range of the detector, the intensity of the electricalsignal is proportional to the intensity of the light. Photomultipliertubes and photodiodes are two types of photodetectors.

Photodiode: A type of photodetector used to detect relatively intenselight signals. It does not have a high voltage applied to increase thecurrent flow at its anode (output) end.

Photomultiplier tube: A photomultiplier tube is a type of photodetectorused to detect a relatively weak signal. Its output current is increasedby means of high voltage applied.

Rotated light scatter: Rotated light scatter (RLS) is a transformationof the data derived from a ratio of the MALS/DC pulse peak information.The RLS function has the effect of removing the size component of thecell, yielding a measurement which is more related to the internalstructure of the cell.

Sheath: Sheath is the fluid within which the central sample core iscontained during coaxial flow from or within the flow cell of a flowcytometer.

Side scatter: Side scatter is light of the same color as theilluminating beam that bounces off particles in that beam and isdeflected to the side. The “side” is usually defined by a lens at rightangle (orthogonal orientation) to the line of the laser beam. It mayalso be alternatively called right angle light scatter or 90° LS. Theintensity of this light scattered to the side is related in a generalway to the roughness or irregularity of the surface or internalconstituents of a particle.

Spatial position: Spatial position is the position of the analyzedpopulation in the domain of analysis. In the example of a VCSinstrument, the domain of analysis is volume measured by D.C. current,high frequency (RF) size and light scatter. Another example is that ifthe analyzed population is only by volume measured by D.C. current, thespatial position would be the mean position of the analyzed populationwithin the D.C. domain.

Threshold: The threshold is an electronic device by which an ADC can bemade to ignore signals below a certain intensity. A forward scatterthreshold is most commonly used in flow cytometry to exclude very smallparticles, debris and electronic or optical noise from acquisition.

VCS technology: An instrument that analyzes blood by using DC (Coulter)volume, Coulter opacity or RF size, and light scatter at various angularranges.

Wavelength: A wavelength is a characteristic of light that is relatedexactly to its energy content and also (with light to which our eyes aresensitive) to its color. Light of short wavelength has more energy thanlight of longer wavelength.

Current multiple white blood cell population analysis requires analogsof specific size and volume increments and specific light scattercharacteristics for use as a quality control. In the method of thisinvention, it is necessary to prepare at least one analog of the majorleukocyte components which are the lymphocytes, monocytes, neutrophils,and eosinophils in order to check the threshold settings of electronicoptical particle counters. Preferably, for the method of this invention,at least a neutrophil analog needs to be prepared. More preferably, aneutrophil and a lymphocyte analog needs to be prepared. Prior hereto,an increased volume was correlated with an increased light scatter whichimpeded the making of at least four different populations of leukocyteanalogs from other than human white blood cells. As the analogs andinstruments used to analyze the analogs have become more complex, thesuspension media for the analog has to compliment their complexity. Morespecifically, the suspension media must be compatible with these analogsand instruments, and compliment the physical and biological propertiesof the analogs.

The suspension media is primarily used with leukocyte analogs producedfrom blood cells. One process to produce leukocyte analogs providestreated blood cells from different sources to match a plurality ofthreshold settings for many types of blood counting instruments. In theselection of the blood cells, the main limitation is the mean cellvolume of the original cells as it relates to the mean cell volume ofthe desired analog. Without limiting the scope of this method, specificreference will be made to blood cells from particular animals, with theunderstanding that red and white blood cells from other animals may beemployed in the method of this invention.

One process for the manufacture of the leukocyte analogs that are usefulin the method of this invention comprises mixing a red blood cell with ahypoosmotic solution to expand the volume of the cell; changing thehemoglobin content of the cell to simulate the light scatter and opacityproperties of human leukocyte cells; and, fixing the cell so that it isresistant to degradation by lytic reagents used in the hematologicaltest procedure and said fixed cell having at least two propertiesselected from the group comprising volume measured by D.C. current, highfrequency (RF) size, opacity and light scatter similar to humanleukocytes properties. The process for making the eosinophil blood cellanalog is similar, but the changing of the hemoglobin content isaccomplished by denaturing it in the cell rather than leaking it fromthe cell. This additional embodiment results in an analog having volumeand light scattering characteristics of a human leukocyte.

This process also enables the swelling of red blood cells greater than50% of their original volume, which provides a wider latitude in theselection of animal cells for producing the desired analogs. In apreferred process, the red blood cells are swollen greater than 75% oftheir original volume.

For the purpose of making analogs suitable for use with the method ofthis invention, it has been found that fowl red blood cells such asturkey, chicken, duck, and preferably goose red blood cells, lendthemselves to an aldehyde stabilization process to produce the smallerlymphocyte analogs. It has also been found that other non-humanvertebrates including “fishes”, particularly members of the sharkfamily, and reptiles, preferably alligators, have red blood cells in thedesired size range which when properly treated yield in an analogsimilar to the larger sizes of the human monocytes, neutrophils andeosinophils. These erythrocytes generally show excellent suspensionstability and highly reproducible volume distribution characteristics.However, considerations, such as availability in quantity at reasonableexpense, must be considered.

Moreover, the red blood cells are fixed so that they are resistant todegradation by the lytic reagent used in the hematological testprocedures when determining the white blood cell parameters in the wholeblood control product.

The cells of avian, alligators and nurse sharks, are nucleated, but thepresence of a nucleus is neither essential nor detrimental for their useas a substitute for human white blood cells, given the process describedherein which permits a regulated hemolysis of the red blood cell.Preferably between 20% to 80% by weight and most preferably 30% to 70%by weight of the hemoglobin in the cell is released. The cells arefurther stabilized with a fixing agent, such as an organic aldehydewhich prevents disruption of the cell membrane and further loss ofhemoglobin.

Another process for the manufacture of the leukocyte analogs that areuseful in the method of this invention includes the stabilizing of humanwhite blood cells to simulate at least one of the five subpopulations ofleukocytes.

In addition, the method of this invention is useful with leukocyteanalogs prepared by other processes known in the art. These stabilizedleukocyte analog cells provide a satisfactory substitute for humanleukocyte cells in a control product.

A preferred process to produce a control product suitable for use in themethod of this invention, embodies a composition prepared by mixing asuspension of fixed goose red blood cells to simulate human lymphocytes,fixed alligator red blood cells to simulate human monocytes,neutrophils, and eosinophils, all assembled in the suspension media andin such proportions as to provide a single composition to simulate humanwhite cells. This control product then is commingled with lysable humanred blood cells, and stabilized platelets or platelet analogs, toprovide a single multiple-analysis control product.

The following description describes a preferred process of making acontrol product using red blood cells for use in the method of thisinvention.

In the collecting step, the red blood cells are suspended in ananticoagulant, such as an alkali metal salt ofethylenediaminetetraacetic acid (EDTA) dissolved in a physiologicalsaline solution (sodium chloride). It is envisioned that otheranticoagulants and salts will do, as long as they do not cause unduehemolysis or cell association.

Fresh red blood cells must be washed to remove donor specific plasmaproteins. This will reduce the probability of cell agglutination whenmixing red cells from multiple blood cell donors. The cells are pooledtogether to obtain a homogeneous composite.

The cell pool may be pretreated with a serum substance as a processingaid. The pretreatment with the serum substance permits swelling of thecell without causing the cell to rupture. Exposure of the erythrocytesto a hypoosmotic environment has the principal effect of increasing themean corpuscular volume, and decreasing the widths of the light scatterhistogram. The blood cells are increased in size as a result of thehypoosmotic environment having a solute concentration which is reducedfrom the solute concentration of the cells. When the concentration ofsolute inside the cell is greater than the concentration outside thecell, there is a tendency for the water to move into the cell toequilibrate concentration. As such, the moving of water inside the cellcauses swelling. The hypoosmotic environment can include a solution ofsodium compounds, potassium compounds, or both sodium and potassium orother compositions known to those skilled in the art to provide thedesired solute concentration.

As defined herein, serum comprises cholesterol, cholesterol esters, andcholesterol which has been combined with one or more other compoundsfound in serum plasma, and mixtures thereof. Preferably, such othercompounds further comprise lipoproteins and phospholipids, and mixturesthereof. As appreciated by those skilled in the art, typicallycholesterol will contain approximately 30% esters. As furtherappreciated by those skilled in the art, the lipoprotein will maintainthe cholesterol in an aqueous solution. Preferably, the serum substancein the pretreatment is selected from the group comprising cholesterol,cholesterol esters, lipoprotein cholesterol, lipoprotein cholesterolesters, cholesterol combined with phospholipids and mixtures thereof.Most preferably, the serum substance comprises cholesterol incombination with phospholipids. A suitable commercially availableexample of such preferred embodiment is Pentex® Cholesterol Super-Trateby Miles, Inc., which is a high density lipoprotein cholesterol andlipoprotein cholesterol esters in combination with phospholipids. Thus,when smaller cells are expanded greater than 30% to 50% of theiroriginal volume, the pretreatment is necessary. It is further believedthat the concentration of the serum substance used is both a function ofthe amount of cell expansion, caused by the hypoosmotic solution, aswell as, the process conditions of the fixation reaction which permitsthe cell's hemoglobin to leak from the cell. In processes which fix thecell in less than approximately 2 hours due mainly to the aldehydeconcentration at room temperature, and wherein the hypoosmotic pressureis greater than approximately 150 milliosmoles, no pretreatment appearsnecessary. When the pretreatment is used, preferably the concentrationof the cholesterol is from 0.1 to 5.0 milligrams to a cell count of1×10⁶ cells per microliter. If too high of a cholesterol concentrationused, then the cells will tend to lyse. If too low of cholesterolconcentration is used, the cell will rupture when swelled.

Prior art attempts at swelling cells without bursting them have focusedon the use of a processing aid, such as potassium sodium tartrate, whichfunctions to strengthen the cell membrane. However, this approach doesnot permit expansion greater than the expected 30 to 50%, nor providethe cell with regulated hemolysis.

Although the present process is disclosed in terms of simultaneouslyswelling and fixing of the cell in a one step process, it is within thecontemplation of this process that more than one step could be used topretreat the cell with the serum substance, swell the cell to permit acontrolled release of hemoglobin and thereafter fix the cell. However,such procedure would be expected to have the problems of controlling theprocess conditions for each step, and more specifically, the timing ofthe fixation of the blood cell.

In a preferred process to produce the control product for use in themethod of this invention, the hypoosmotic solution is formed bycombining an aqueous solution of sodium phosphate with the fixativereagent to the desired osmotic pressure. The lower the osmotic pressurerelative to the normal tonicity of the native blood, the more that thecell will swell due in part because of the water moving from outside thecell to inside the cell. The osmotic pressure will preferably range from0 to 150 milliosmoles, depending upon the initial cell size, cell count,and the desired final cell size; even more preferably from 65 to 95milliosmoles for the eosinophil analog; 0 to 20 milliosmoles for themonocyte analog; 5 to 35 milliosmoles for the lymphocyte analog; andfrom 45 to 65 milliosmoles for the neutrophil analog. The abovepreferred ranges are based upon blood cells that have been washed withan isotonic saline solution and are further based upon a cell count inthe fixative reaction of approximately 20,000 to 50,000 cells permicroliter.

Concomitantly, temperature does not appear to independently affect theswelling rate of the cell, but does affect the rate of the fixationreaction. As the cell expands, the hemoglobin leaks out of the cell at acontrolled rate until the fixation reaction prevents further release ofhemoglobin. The majority of the hemoglobin will be released within thefirst five minutes of the hypoosmotic treatment. Thus, in thesimultaneous swelling and fixing of the cells, reducing the temperatureof the fixation in solution enables the control of the fixation processand hemoglobin release rates during which time the cell is swelling.Upon completion of the fixation reaction, the cell is resistant todissolution or degradation under the influence of the usual lysingreagents used in hematological test procedures.

In a further process to produce control products for use in the methodof this invention, the blood cells are added to a chilled hypotonicsolution containing glutaraldehyde. The chilled fixing solution is at atemperature of 0° to 15° C., and more preferably, from 1° to 10° C.,most preferably, the fixation treatment is at 2° to 8° C. for thelymphocyte and monocyte analogs and at room temperature for theneutrophil and eosinophil analogs. The reduced temperature has beenshown to provide a qualitatively different cell as measured on a sizingapparatus such as a COULTER COUNTER® Model VCS analyzer. A qualitativedifference includes a higher mean cell volume compared to fixing at roomtemperature.

Fixing of the swollen cells is important to toughen the cell membranesand to prevent degradation of the membranes. This is accomplished bycontacting the cells with a solution of an organic aldehyde, includingmonoaldehydes such as formaldehyde, or dialdehydes such asglutaraldehyde. Glutaraldehyde is the preferred aldehyde, since itreacts more speedily than formaldehyde. Glutaraldehyde can be added inhigher concentrations than the final concentration, so long as the finalconcentration is in the range of about 0.05% to 0.8% and more preferably0.1% to 0.6%, based upon a cell count of approximately 20,000 to 50,000cells per microliter. The practical limitations on selection of anappropriate aldehyde and concentration thereof are the functionallimitations of the number of cells, elimination of undue cellassociation, and as a parameter in controlling the fixation reaction.The fixation reaction conditions will vary for the specific animal cellused and the leukocyte analog being manufactured.

Although most room temperature fixation with glutaraldehyde occurswithin two hours, more time is required for the red blood cells to betotally resistant to the usual red blood cell lytic agents employed inCOULTER COUNTER® hematology instruments. With careful selection of thered blood cells, the length of time for fixation with glutaraldehydewill range between 2 and 72 hours, preferably between 3 to 30 hours,depending upon temperature, concentration of glutaraldehyde, number ofcells and desired amount of hemoglobin released. In a most preferredembodiment, the fixation time for a cell count of approximately 20,000to 50,000 cells per microliter is between 10 to 24 hours for themonocyte and lymphocyte analogs and 3 to 18 hours for the eosinophil andneutrophil analogs. Under-fixation may result in a partially fixed redblood cell with a mean cell volume less than that for the targeted humanleukocyte population. Generally, the upper time limit of fixation isbased upon manufacturing convenience. After fixation, the cells areseparated from the liquid phase by a centrifugation or gravitation meansand then are washed with a phosphate buffered saline solution.

The pH of the fixing solution ranges from 7.0 to 9.0. If the pH of thefixing solution is too low, agglutination may occur; and if too high,the cell may rupture. In addition, the pH affects the release ofhemoglobin. If the fixation reaction occurs too quickly, the cell willnot be able to leak the hemoglobin. Thus, the pH range is approximately7.0 to 9.0, and preferably 7.5 to 8.5. In a most preferred embodiment,the pH of the fixation solution is 8.0±0.2 for the neutrophil andeosinophil analogs, and 7.8±0.1 for the monocyte and lymphocyte analogs.

The eosinophil analog is prepared in a similar process except, thehypotonic glutaraldehyde solution is preferably at room temperature andthe hypotonic glutaraldehyde solution is primarily used to lightly crosslink the hemoglobin in the blood cells, rather than to completely fixthe cell. As such, the glutaraldehyde concentration for a cell count ofapproximately 20,000 to 50,000 cells per microliter is betweenapproximately 0.1 and 0.4%, and more preferably from 0.2 to 0.3%. Afterlightly cross linking the hemoglobin and washing with a phosphatebuffered saline solution, the cells are further treated with a proteindenaturing reagent, such as a quaternary ammonium compound, or otherdenaturing agent known to those skilled in the art to precipitate thehemoglobin within the cell. The pH of the denaturing solution should bebetween 9.0 and 12.0, and preferably between 10.0 and 11.0. Thistreatment does not reduce the volume of the cell. The treatment with theprotein denaturing reagent increases the light scatter characteristicsof the swollen cell to provide the swollen cell with the requisite lightscattering characteristics similar to the human eosinophil. Both thedenaturation of the hemoglobin and the controlled release of thehemoglobin have the effect of changing the hemoglobin composition in thecell. However, the light scatter properties are distinctly differentbetween the controlled release of the hemoglobin in the monocyte andlymphocyte analogs and the denaturation of hemoglobin in the eosinophilanalog. Generally, the leaking of hemoglobin from the cell will reducethe light scatter and opacity of the cell. Denaturing the hemoglobin inthe cell will increase the light scatter of the cell.

The preferred process of preparing the eosinophil analog comprisespretreating the red cell pool with an aqueous serum substance, swellingthe cell, denaturing the hemoglobin in the cell and fixing the cell. Asappreciated by one skilled in the art, it is within the contemplation ofthis process to produce a control product that one could choose anappropriate sized red blood cell which did not require the amount ofswelling which would necessitate the pretreatment with the serumsubstance. In such case, the process would comprise denaturing thehemoglobin in the cell to simulate the light scatter properties of ahuman leukocyte cell and fixing the cell so that it is resistant todegradation by lytic reagents used in hematological test procedures. Assuch, the treated red cell would have light scatter and volumeproperties similar to human leukocytes. However, if the cell is notswelled to some extent, it would be expected that since the red bloodcell is not by nature spherical, the standard deviation of the lightscatter would not be within boundary of the targeted cell population.The addition of a sphering agent may obviate this problem.

By using a combination of the above disclosed processing steps, ofswelling the cell, leaking of hemoglobin from the cell, denaturing thehemoglobin in the cell, as well as, shrinking the cell by processesknown to those skilled in the art, one is effectively provided withprocesses to design an analog having a plurality of different physicalparameters of D.C. volume, RF size, opacity and light scatter which canbe used in new methods to diagnose the cause of a malfunction of aninstrument. More specifically, shrinking and swelling of the cell canaffect all of the above listed parameters, while changing the hemoglobinin the cell can affect the opacity and light scatter characteristics.

The suspension media disclosed herein, is also used with leukocyteanalogs prepared by other processes known in the art. One such otherprocess includes the fixing of human white blood cells to simulate fivesubpopulations of leukocytes as described in Example 5 herein.

The reference blood cell control product can include one or more of theleukocyte analogs prepared by any process known to those skilled in theart or any of the above described processes. The leukocyte analog can bestored in any suitable media such as phosphate buffered saline solutionand those fully described in U.S. Pat. Nos. 4,213,876; 4,299,726,4,358,394 and 3,873,467.

The following specific example is disclosed in U.S. Pat. No. 4,299,726:

Stabilizing Media for Conferring Long Term Stability on Red BloodCells-Preferred Formulation Approximate Amounts Liter Formulation 1.Distilled water 500 ml 2. Propyl paraben 0.3 to 1.0 gm 3. Methyl paraben0.5 to 1.0 gm 4. Procaine hydrochloride 0.1 to 0.5 gm 5. Deoxycholicacid 0.1 to 0.9 gm 6. Lactose 10.0 to 50.0 gm 7. Actidione 0.1 to 0.6 gm8. Trisodium citrate dihydrate 3.0 to 8.0 gm 9. Citric acid monohydrate0.3 to 0.9 gm 10. Sodium dihydrogen phosphate 0.8 to 2.5 gm monohydrate11. Phenergan hydrochloride 0.1 to 1.0 gm 12. Colistimethate, sodium 0.2to 0.9 gm 13. Penicillin G., sodium 0.5 × 10⁶ to 3 × 10⁶ units 14.Kanamycin sulfate 0.2 to 0.8 gm 15. Neomycin suifate 0.2 to 1.0 gm 16.5′-AMP 0.4 to 1.0 gm 17. Adenine 0.2 to 0.8 gm 18. Inosine 0.4 to 1.0 gm19. Dihydrostreptomycin sulfate 0.2 to 1.0 gm 20. Tetracyclinehydrochloride 0.2 to 1.0 gm 21. 30% Bovine albumin 100 to 350 ml 22.q.s. to 1 liter with distilled water

Since many of the chemicals listed above are known commercially byseveral names, the name given is a common name listed in the MerckIndex, Eleventh Edition (1989), published by Merck and Co., Inc.,Rahway, N.J.

When making the control product, the supernatant fluid is removed fromthe leukocyte analogs and they are then resuspended in the suspensionmedia. The preferred suspension media comprises an aqueous solution of aplasma substance. As defined herein, an aqueous solution of a plasmasubstance comprises an aqueous solution of a serum substance (aspreviously defined), serum substance in combination with a plasmaprotein and mixtures thereof. As further defined herein, plasma proteincomprises one or more of the proteins contained in plasma. Preferably,such plasma proteins comprise albumin, lipoproteins, globulins,fibrinogens, and mixtures thereof. More preferably, the plasma substanceis selected from the group comprising cholesterol, cholesterol esters,lipoprotein cholesterol, lipoprotein cholesterol esters, cholesterolcombined with phospholipids, cholesterol combined with albumin,cholesterol esters combined with albumin, lipoprotein cholesterolcombined with phospholipids, lipoprotein cholesterol combined withalbumin, and mixtures thereof.

To confirm the utility of the plasma substance for red blood cell lysisin a saponin based lytic system, an aqueous plasma substance was addedto washed red blood cells. The aqueous solution comprised 3% plasmasubstance in a phosphate buffered saline solution. The results are asfollows:

Sample Plasma Substance Lysis 1. Human albumin Yes 2. Albumin with fattyacid removed No 3. Sample 2 with lipoprotein cholesterol Yes 4. Bovineserum albumin No 5. Sample 4 with lipoprotein cholesterol Yes 6. Albuminbound cholesterol Yes 7. Monomer albumin Yes 8. Bovine serum albumincapalate stabilized No 9. Sample 8 with lipoprotein cholesterol Yes 10.Polymer enhanced bovine serum albumin Yes 11. Human albumin Yes 12.Swine albumin Yes 13. Media of U.S. Pat. No. 4,299,726 No 14. Sample 13with lipoprotein cholesterol Yes 15. Cholesterol bound with a surfactantNo 16. Phosphate buffered saline (PBS) solution No 18. Lecithin No 19.PBS with lipoprotein cholesterol Yes

From the test results given above, it has been determined that theaddition of a plasma substance to washed red blood cells enables lysisin a saponin lytic system. It is believed that the albumin isinteracting with the red blood cell and saponin to effect the lyticaction. However, when the washed red blood cells and bovine serumalbumin are further combined with other ingredients such as thosedisclosed in U.S. Pat. No. 4,299,726, the albumin does not cause thelysis. However, when a lipoprotein cholesterol is added, lysis iseffected. Moreover, when a lipoprotein cholesterol is added to the PBS,lysis is effected.

When using the leukocyte analogs prepared from red blood cells asdescribed above, the aqueous solution of a plasma substance ispreferably added to the hematological composition at least 12 hoursbefore being used in an instrument. When one or more leukocyte analogsare combined with lysable human red blood cells to provide a singlemultiple analysis reference blood cell control product for instrumentswhich use lytic reagents, it is most preferred that the aqueous solutionof the plasma substance comprises bound cholesterol. A suitable exampleof the most preferred plasma substance is Moducyte®, as described inU.S. Pat. No. 4,290,774, assigned to Miles, Inc., which is a highdensity lipoprotein cholesterol bound with albumen. The finalconcentration of cholesterol in the suspension media ranges from 400 to1,200, and preferably 600 to 1,000 milligrams per liter depending uponthe cell count in the final control product.

For a control product using the leukocyte analogs prepared by thepreferred processes disclosed herein, if an insufficient concentrationof the cholesterol is used in the preferred media, the red blood cellsin the reference blood cell control product will not efficiently lyse todissolve the cell membrane so that there is an absence of noise anddebris when using a saponin lytic reagent system and the leukocyteanalogs will have a mean cell volume below the required size due to thelytic reaction. If the media contains too high of a concentration ofcholesterol, the red blood cells in the reference blood cell controlwill not efficiently lyse to dissolve the cell membrane so that there isan absence of noise and debris.

More specifically, when the control product is used in instruments, suchas those that employ the Coulter Model VCS technology, which uses areagent system such as described in U.S. Pat. No. 4,751,179, in order todistinguish at least two populations of leukocytes, (1) lymphoids(lymphocytes) and (2) myeloids (neutrophils, monocytes, eosinophils andbasophils), the preferred suspension media enables the reaction betweenthe weaker lytic reagent and the non fixed red blood cells to occur sothat the red blood cells lyse while the leukocyte analogs remainsubstantially unaffected, enabling each type of leukocyte analog to becounted. As taught by U.S. Pat. No. 4,751,179, the lysing reagent hastwo forms: (1) a lytic diluent containing saponin, which simultaneouslyfunctions to dilute the whole blood sample and stromatolyse its redblood cells; or (2) a two part system comprised of non-lytic blooddiluent followed by a lytic reagent containing saponin.

When prior art medias, such as those described in U.S. Pat. Nos.4,213,876; 4,299,726; or 4,358,395, are used, the leukocyte analogsprepared by the preferred processes disclosed herein are lower in volumethan desired for the targeted leukocyte population. More specifically,when the preferred suspension media is used with leukocyte analogs,which have been prepared from either red or white blood cells, the D.C.volume of the analog is within the desired range for the targetedleukocyte population.

In a more preferred embodiment, the suspension media would furthercomprise the addition of a non-ionic surfactant. The surfactant willhave a high hydrophile-lipophile balance (HLB). The HLB typically has avalue greater than 15 and more preferably greater than 17. Typically,the surfactant is in an amount effective to make the lytic action morespecific to the red blood cells without detrimentally affecting theleukocyte analogs. In addition, the surfactant will stabilize any freecholesterol in the control product so that it does not separate out insolution. As appreciated by those skilled in the art, the effectiveamount of surfactant may be empirically determined, but is typicallyless than 0.5% by weight of the control product.

Suitable non-ionic surfactants include alkyl polyether alcohols of thegeneral formula: R—X—(Y)_(n)—H, where R is a lipophilic chain C₈-C₁₈carbon atoms; where X is —O—,

—COO—; and Y is CH₂ CH₂O— or CH₂ CH₂ CH₂O; n is an integer of 15-50.Suitable commercial examples of these surfactants include Diazopan®SS-837 by GAF Chemical Corp., Triton® X405 by Rohm and Haas, andPluronic F®-127 PRILL by BASF Wyandotte Corp.

While not desiring to be bound by any theory, it is presently believedthat there is an interaction among the red blood cells, weak lytic agent(e.g., saponin), and the plasma substance in the preferred suspensionmedia causes the red blood cells to lyse. More specifically, it ispresently believed that the plasma substance may be affecting the cellmembrane cholesterol which further affects the leukocyte analog'sresponse to the lytic reagent. Moreover, it is further believed that thesurfactant makes the lytic reaction more specific to the red blood cellsand yet does not detrimentally affect the leukocyte analogs as tomeasured control parameters. In addition, it is further believed thatthe surfactant may also be affecting the cholesterol found in the cellmembrane or in the plasma substance.

The preferred suspension media for the hematological reference controlproduct having stability up to six months includes an aqueous solutionof the plasma substance and optional compatible fungicidal andbactericidal agents, and optional supplementary agents such as purinenucleoside, bile salt, and cholic acid derivatives, phenothiazinecompounds and the salts thereof having antihistamine properties, and4-aminobenzoic acid esters and derivatives and their salts havingaesthetic properties, as well as, sphering agents for the red bloodcells, or combinations thereof. Since one or more of the leukocyteanalogs may be combined into a single reference blood cell controlproduct for use with the known lysing agent for the red blood cells, theformulation for the preferred suspension media is the same for all ofthe leukocyte analogs.

As appreciated by one skilled in the art, the suspension media shouldhave sufficient tonicity to avoid cell lysis. The preferred formula forthe suspension media is:

Suspension Media Approximate Amounts Liter Formulation 1. Distilledwater 500 ml *2. Propyl paraben 0.3 to 1.0 gm *3 Methyl paraben 0.5 to1.0 gm *4. Procaine hydrochloride 0.1 to 0.5 gm *5. Deoxycholic acid 0.1to 0.9 gm *6. Lactose i0.0 to 50.0 gm *7. Actidione 0.1 to 0.6 gm *8.Trisodium citrate dihydrate 3.0 to 8.0 gm *9. Citric acid monohydrate0.3 to 0.9 gm *10. Sodium dihydrogen phosphate 0.8 to 2.5 gm monohydrate*11. Phenergan hydrochloride 0.1 to 1.0 gm *12. Colistimethate, sodium0.2 to −0.9 gm *13. penicillin G., sodium 0.5 × 10⁶ to 3 × 10⁶ units*14. Kanamycin sulfate 0.2 to 0.8 gm *15. Neomycin sulfate 0.2 to 1.0 gm*16. 5′-AMP 0.4 to 1.0 gm *17. Adenine 0.2 to 0.8 gm *18. Inosine 0.4 to1.0 gm *19. Dihydrostreptomycin sulfate 0.2 to 1.0 gm *20. Tetracyclinehydrochloride 0.2 to 1.0 gm *21. 30% Bovine albumin 100 to 350 ml 22.Lipoprotein Cholesterol 400 to 1,200 mg 23. q.s. to 1 liter withdistilled water *Optional ingredient preferred for conferring long termstability for red blood cells and analogs.

The manufactured control product can be used to monitor and diagnose thecause of a malfunction of an instrument. In this invention, a method forusing a hematology control product has been developed that enables themonitoring and diagnosing of an instrument for problems associated with:

1. lysis debris and noise

2. instrument reagents pump volume settings

3. instrument laser alignments

4. instrument gain settings

5. inconsistency of flow rate in the flow cell

The method provides a more specific indication of the type and cause ofan instrument malfunction than non specific flagging that isdiagnostically non specific or inspection of the test results by theinstrument operator which are provided by prior art methods. Thefollowing description describes a new method of using the previouslydescribed control product. As appreciated by one skilled in the art, thecontrol product must contain lyseable erthryocytes to monitor anycellular debris and noise caused by ineffective red cell lysis. Themethod uses new control parameters of the physical properties of thecontrol product to determine the cause of an instrument malfunction.These physical properties are selected from the group comprising:

(1) volume measured by D.C. current,

(2) high frequency (RF) size,

(3) opacity, and

(4) light scatter.

The leukocyte populations are used as the indicator of systemperformance. Preferably the neutrophil and lymphocyte subpopulations areused as control parameters and are measured to determine instrumentperformance. More preferably the neutrophil population is used as acontrol parameter and is measured as an indication of systemperformance.

In order to determine whether there is a noise problem due to cellulardebris, the use of two control parameters are employed. The controlparameters are COUNT RATIO and ELAPSED TIME. The COUNT RATIO is ameasure of the number of white blood cells in an analysis compared tothe total count of events that are recorded in the analysis during aspecific ELAPSED TIME. ELAPSED TIME is a measured period of time,usually in seconds. As the ratio of white blood cells counted and totalevent counted approaches 100 percent, the cellular debris or noiseproblem associated with an instrument malfunction is eliminated.

An example of the use of COUNT RATIO in an instrument employing VCStechnology would be a comparison of the number of white blood cellsanalogs compared to a total count of 8192 particles obtained for aspecific ELAPSED TIME. If the ratio is less than about 95%, there is anindication that noise or interference is a problem. The specific problemis further confirmed by additional tests that are further explained inthis disclosure.

Another approach to monitor and diagnose an instrument for problems isto use fresh blood monitoring of the running average of the same set ofparameters of a statistically significant number of patient normalbloods. When the average is outside the expected ranges of the controlparameter there is an early indication of the instrument malfunction.The instrument malfunction can be further verified using the controlproduct described herein.

One indication of whether an instrument is properly functioning is todetermine the cellular debris or noise that is measured by theinstrument. Excess cell debris can be caused by incomplete lysis,changes in the reaction kinetics due to temperature conditions orinterference with the lytic reaction. Since various instrument systemshave cell count and data accumulation time limitations, excess debris ornoise from any source interferes with the proper acquisition andanalysis of the white cell populations. The cause of the cellular debrisor noise problem can be attributed to several problems including:

A. conductivity noise due to sheath fluid and the blood sample streamimbalance.

B. Lysing noise caused by improper red cell lysing.

C. Flow noise caused by partial plugs, residual plugs or other flowproblems

In order to determine whether the malfunction is due to conductivitynoise caused by mismatches between the sample stream and the sheathfluid stream conductivity, one first measures the reagent pump volumes.A calibrated container is employed to measure each of the reagents thatare added to the blood sample. The volume of reagent that is transferredshould be within a predetermined value. If the volume of a reagent isnot within the prescribed limits, then the reagent pump is adjusted toincrease or decrease the reagent volume that will be dispensed.

In the example of an instrument that employs VCS technology, onemeasures the pump volumes of the lytic reagent and quench reagentstreams. A calibrated container is employed to measure each of thesevolumes. The volume of the reagent should be within a predeterminedvalue. If the volume of the reagent is not within the prescribed limits,then the pump is adjusted to increase or decrease the volume that willbe provided.

The prepared control product containing fixed cell analog populationsthat are osmotically sensitive are further used to monitor the reagentpump volumes. Changes in volume of lytic reagents will affect the finalosmolality of the diluted blood sample and affect the measured volume ofthe analog population. Lower osmolality increases the measured volume ofthe control cell analog and higher osmolality decreases the measuredvolume of the control cell analog. Variations of reagent pump volumesbeyond the limits of conductivity required to electrically balance thesheath fluid will produce noise in addition to the changes in the volumeof the control cell.

Therefore, after the conductivity noise has been minimized by thepreceding process, lysing noise resulting from improper red cell lysingis checked with a control product containing a known number ofstabilized red blood cells and at least one leukocyte analog cellsubpopulation. If lysing is a problem, then the control cells will showa COUNT RATIO less than about 95% of the maximum COUNT RATIO. Inaddition, although the reagent volumes can be adjusted by the precedingprocess, the lysing kinetics relating to the temperature of the lysingreaction will be affected. More specifically, it has been found that ifthe room temperature of a laboratory instrument is at 50° F., the lysingreaction will require a different lytic and quench reagent volume thanif the temperature is at 90° F., to obtain a minimum of lysing noise.

In the example of an instrument which employs the VCS type technology,the lytic reagent and quench reagent are reacted with a blood sample toprovide a lysed and diluted suspension of white blood cells suitable formeasurement. In the VCS type instrument, blood cells are reacted withthe lytic reagent causing hypotonic cell swelling, red cell and plateletlysis and dissolution of red cell and platelet membranes. Reaction withthe quench reagent stops the swelling and lysis and begins a process ofre-equilibration of the white cells to their native size. Because of thenature of the reactions, the lytic reagent and quench reagent are verydifferent in both osmolality and conductivity. The final osmolality andconductivity of the sample stream is proportional to the volume,osmolality and conductivity of the lytic reagent, quench reagent andblood sample.

The use of two control parameters are employed to determine if thereagent pump volumes are within specification or determining the causeof the malfunction. The monitoring the COUNT RATIO and NEUTROPHIL DCMEAN assists one in differentiating pump volume changes withinconductivity tolerances and beyond conductivity tolerances. TheNEUTROPHIL DC MEAN is the neutrophil mean value in the DC channel.

Another approach to monitor and diagnose an instrument for problems isto use fresh blood monitoring of the running average of the same set ofparameters of a statistically significant number of patient normalbloods. When the average is outside the expected ranges of the controlparameter there is an early indication of the instrument malfunction.The instrument malfunction can be further verified using the controlproduct described herein.

It has been found that the COUNT RATIO of the white blood cells isrelated to the reagent pump volumes calculated from known reagentconcentrations and measured pump volumes, expressed as either dilutionconductivity or osmolality. FIG. 1 represents a comparison of the COUNTRATIO of the white blood cells compared to the conductivity of thediluted blood sample in the diluted blood sample stream that is to betested. As shown in FIG. 1, as the quench reagent volume is increased,the COUNT RATIO increases to a plateau. When the quench volume isincreased beyond the optimum range the COUNT RATIO is substantiallyreduced.

To obtain a comparable FIG. 1 using a control product, the lytic reagentvolume is provided at a first volume that would be expected to provideproper lysis. The quench volume is adjusted from providing insufficientquench reagent to providing an excess amount of quench reagent. When thequench reagent volume is insufficient, the COUNT RATIO is significantlyreduced. As the quench volume is increased the COUNT RATIO rises andplateaus over the optimum performance range. Increasing the quenchvolume above the optimum range causes the COUNT RATIO to besubstantially reduced. Upon obtaining this information, the pump for thequench reagent can be adjusted to provide a quench reagent volume thatis in the middle of the plateau.

After the quench volume has been adjusted, the lytic reagent pump can bere-adjusted. It has been found that the NEUTROPHIL DC MEAN of thecontrol product is related to the lytic reagent pump volume. Themonocyte population shows sensitivity similar to the neutrophilpopulation. The pump for the lyse reagent is adjusted to provide anosmolality which corresponds to a previously measured NEUTROPHIL DC MEANof the control product. The previously measured NEUTROPHIL DC MEAN isprovided as an assay value from a reference instrument.

FIG. 2 represents a comparison of the NEUTROPHIL DC MEAN compared to theosmolality of the blood sample being analyzed after it has been dilutedwith the lytic and quench reagents. As shown in FIG. 2, as theosmolality is increased, the NEUTROPHIL DC MEAN of the control productdecreases.

In order to determine whether there is a problem because of left overplugs or partial plugs, two control parameters of WHITE TIME and DATETIME are used. The monitoring of these two control parameters assistsone in determining these type of problems. WHITE TIME is the product ofthe number of white blood cell analogs multiplied by the time requiredfor analysis. DATE TIME is the day that a control sample has beenanalyzed. It has been found that using these two control parameters on aroutine basis with a control product that contains a known number ofleukocyte analogs provides information as to instrument performanceproblems.

In the method of this invention, the control product is used at leastdaily. The WHITE TIME and DATE TIME are recorded to provide meaningfulinformation about the existence of flow problems. More specifically,when the WHITE TIME is graphed versus the DATE TIME, one is able toobtain a two dimension graph of the performance of the instrument todetermine trends of the flow performance of the instrument.

In a VCS type instrument, an alternate method is provided to check thesample flow rate. The VCS instrument records the WHITE TIME and DATETIME on each patient blood sample that has been analyzed by theinstrument. By comparing these control parameters on a statisticallysignificant number of patient blood samples, an expanded data base isavailable to monitor the history of the instrument's flow performance.More specifically, by recording the WHITE TIME and DATE TIME on eachpatient blood sample, one is able to detect whether left over plugs orpartial plugs have occurred. Left over plugs can restrict the flow ofsubsequent samples, but may produce no detectable change in the numberof cells per second. Partial plugs can increase the time required toobtain the white blood cell count because of a reduced flow of cellsthrough the flow cell.

In addition, when these control parameters are monitored for the patientsamples, a two dimension analysis can be obtained to discover if theflow rate is deteriorating and whether noise and debris levels areinterfering with the expected time to obtain the white blood cell count.Excessive debris will decrease the amount of time necessary to obtain aspecified number of white blood cells. This two dimensional analysis hasprovided an improvement over complex multidimensional analysis of theprior art.

Prior art methods to determine problems due to the consistency of theflow cell has been to measure the number of leukocytes that are detectedduring a predetermined time. More specifically, the instrument operatorwould use a specially selected fresh blood that had a known number ofwhite blood cells and measure the time the instrument required to detectthe white blood cells. If the instrument detected the white blood cellswithin a specified time, it was presumed that there was an absence offlow cell problems. However, this measurement only provided informationabout the instrument for that particular analysis. This measurement didnot provide meaningful information concerning the performance of theinstrument over an extended time period. More specifically, graphing thecount of white blood cells per unit time only provides an instantaneousview of the instrument's performance on that one day. To obtain a viewof the performance of an instrument over several days, a threedimensional charting of the results was necessary. Moreover, the methodof this invention uses a control product with a known number of whiteblood cells which eliminates the necessity of obtaining a speciallyselected fresh blood and determining the number of white blood cells itcontains.

In addition, a control product can be used to monitor the instrument todetermine if there is a problem with the instrument's laser, the laseroptics or the laser alignment. Laser alignment has three dimensionswhich corresponds to X, Y and Z axes.

Currently, the material used to set and then monitor laser alignment andgain adjustments is latex microparticles. The method of using the latexparticle is to monitor the population mean and coefficient of variationof the latex population. However, if the laser lens accumulates dirt orother debris which obscures the laser beam signal, the prior artpractice has permitted obscuring the alignment problem by increasing thegain of the laser to overcome the interference to the laser beam. Inaddition, the latex particles are not responsive to the reagents thatare used in the instrument. Moreover, the latex particles are a separatecontrol product that is required to be run in a calibration mode in theinstrument. The latex particles require additional work to be undertakento monitor instrument's performance. Therefore, it is advantageous tohave a single hematological control product that is both responsive tothe reagents used in the instrument and provides and indication of theperformance of the laser in the instrument.

It has been determined that X-axis alignment is the most sensitive ofthe axes and produces the greatest affects on a control product's lightscatter position and distribution. The rotated light scatter position ofthe control product is at a maximum when the X axis is properly alignedand the distribution width is at its minimum. As the alignment degradesto slight misalignment and then to gross misalignment, the controlproduct's position in the histogram shifts to the left, the mean valuedecreases and the rotated light scatter channel distribution widens.

When analyzing fresh blood and having X-axis misalignment, the whitecell populations are shifted left (low light scatter) producing a lossof white cells counted and an increase in noise. As misalignment becomesmore extreme, the effect on fresh blood analysis is that thesubpopulations of leukocytes merge and differentiation is lost.

Y-axis and Z-axis misalignment do not show the same kind of change ofposition of the white cell population as exhibited by the white bloodcells when caused by X-axis misalignment. It has been determined thatZ-axis alignment is related to whether the lens is in a proper focallength which will provide the sharpest image. If the Z-axis ismisaligned, then the resulting scatterplot will not have clear distinctclusters of leukocytes. More specifically, in a histogram of lightscatter versus DC volume, the separation of the populations oflymphocytes and monocytes, from the population of neutrophils will notbe distinct. There will be a degradation of the separation of the lightscatter peaks of the volume populations. More specifically, there willbe a reduction in the individual populations in amplitudes and anincrease in the amplitude of the valleys between the populations.

It has been found that the lymphocyte population of the control productprovides information to determine low light scatter while the neutrophilpopulation provides information to determine high light scatter. Therelationship between the position of these two populations monitorssystem variables that produce both bias and proportional effects onpopulations position such as laser alignment (bias) and DC, RF and LSgain (proportional) adjustments.

The use of two control parameters can be employed to determine theproblem with the laser's operation. The monitoring of the NEUTROPHIL RLSMEAN and the PEAK TO VALLEY RATIO will provide an indication of theperformance of the laser and X axis and Z axis alignment. The LYMPHOCYTERLS MEAN shows sensitivity similar to the NEUTROPHIL RLS MEAN. TheNEUTROPHIL RLS MEAN is the neutrophil mean value in the light scatterchannel. The LYMPHOCYTE RLS MEAN is the lymphocyte mean value in thelight scatter channel. The PEAK TO VALLEY RATIO (PVR) is the ratio ofthe amplitude of the rotated light scatter signal of the neutrophilpopulation compared to the rotated light scatter signal of the valleyformed between the lymphocyte and monocyte populations, and theneutrophil population.

The PVR provides a reliable quality control parameter to be used in amethod to determine whether a problem exists with the laser. When usinga control product the PEAK TO VALLEY RATIO should meet a thresholdnumber which has been predetermined. If the PVR meets or exceeds thisnumber, the laser is operating optimally. More specifically, a PVR thatmeets the predetermined number indicates that there is a clearseparation of the neutrophil population and lymphocyte and monocytepopulations. If the PVR is less than the predetermined number, thenthere is an indication that a problem with the laser exists.

As previously noted, the prior art practice has permitted increasing thelaser gain to compensate for a dirty lens. However, a latex particlecontrol does not provide specific information concerning themisadjustment of the light scatter signal gain when optical interferenceexists. It has been determined that when the gain adjustment has beenimproperly increased that the entire neutrophil population position inthe rotated light scatter histogram, including the NEUTROPHIL RLS MEAN,is shifted to the right.

In accordance with the method of this invention, the determination of aPVR that is less than the predetermined value, and the NEUTROPHIL RLSMEAN is above the predetermined value, it indicates that the instrumenthas a problem with either optical interference or X-axis or Z-axisalignment. Therefore, the technician will know to clean the lens andcalibrate the laser alignment. In addition, it has also been determinedthat if the determination of a PVR that is less than the predeterminedvalue, and the NEUTROPHIL RLS MEAN is below the predetermined value, itindicates that the instrument has a problem with either opticalinterference which has not been compensated by increasing the gain orX-axis or Z-axis alignment. Moreover, if the PVR is within thepredetermined value and the NEUTROPHIL RLS MEAN is either greater thanor less than the predetermined value, it indicates that the laser gainis set improperly. Still further, if the PVR is below the predeterminedvalue and the NEUTROPHIL RLS MEAN is within the predetermined value, itindicates that the laser needs replacing because it is losing power.

While the foregoing specification explains the use of some of thecontrol parameters to determine whether an instrument is performingaccording to manufacturer's specification and the use of the controlparameter to diagnose the cause of the malfunction, Table 1 provides adetailed analysis of which control parameters can be used for a controlproduct or for a statistically significant value of patient bloodsamples to detect and diagnose problems with an instrument's system. Inthis Table, the following abbreviations are used:

s=sensitivity for the applicable instrument function

SD=standard deviation

OP=opacity

x=measurement of Control Product or Sample

TABLE 1 Patient Control Control Blood Cell/Type Parameter Product SampleLysis Flow Alignment Gain Chemistry Neutrophil DC Mean x x s s DC SD x xs RLS Mean x x s s RLS SD x x s s OP Mean x x s OP SD x x s PVR x sLymphocyte DC Mean x x s DC SD x x s RLS Mean x x s s RLS SD x x s s OPMean x x s OP SD x x s PVR x s Monocyte DC Mean x x s DC SD x x s RLSMean x x s s RLS SD x x s s OP Mean x x s OP SD x x s Latex Particle DCMean x x s Sample DC SD x x s Analysis RLS Mean x x s Mode RLS SD x x ss OP Mean x x s OP SD x x s Noise COUNT RATIO x x s s s Flow WHITE TIMEx x s

In addition, a latex, polystyrene or other plastic bead can be added tothe control product to provide a single reference control product thatcan further indicate instrument performance. More specifically, the useof this type of control product with the control parameters can provideinformation about the instruments performance. For example, if the latexparticle DC gain is within specification, but the control product has aDC mean not within specification, then there is an indication that thereis a problem with the reagent pump volumes.

When this type of control product is used in an instrument that uses VCStechnology, the above described example would indicate that there is aproblem with the lytic or quench reagent volumes. More specifically, inthe VCS type instrument, if the latex particle DC gain is withinspecification, but the control product has a DC mean that is above themanufacturer's specification, then there is an indication that the lyticreagent volume can be above the optimum level or the quench reagentvolume can be below the optimum level. Still further in the VCS example,if the latex particle DC gain is within specification, but the controlproduct has a DC mean that is below the manufacturer's specification,then there is an indication that the lytic reagent volume can be belowthe optimum level or the quench reagent volume can be above the optimumlevel.

The process for preparing leukocyte analogs for use in the method ofthis invention is hereinafter provided in the Examples. Example 1 is aspecific example of preferred reagents and techniques for treating goosecells, it being understood that the formulations are only illustrativeof those that can be used in the method of this invention. Examples 2, 3and 4 are specific examples of preferred reagents and techniques fortreating the alligator cells, it being understood that the formulationsare only illustrative of those that can be used in the method of thisinvention. Example 5 shows an example of using human white blood cellsto produce five subpopulations of leukocyte analogs, it being understoodthat the formulations are only illustrative of those that can be used inthe method of this invention. Example 6 shows an assembly of the fourleukocyte populations. It should be appreciated that these Examplesprovide formulations for the leukocyte analogs which are onlyillustrative. The reagents and/or techniques described can also beapplicable to blood cells from animals other than geese and alligators.Other ingredients and proportions can be employed, in accordance withthis disclosure.

EXAMPLE 1 Lymphocyte Analog from Goose Red Blood Cells

The following is a specific example of preferred reagents andrecommended specific procedural steps for treating goose red blood cellsto obtain a normal sized lymphocyte analog. It will be understood thatthe formulations and the procedures only are illustrative and that otheringredients, proportions and procedures can be employed, in accordancewith the disclosures in this invention.

Phosphate Buffered Saline Solution (PBS) Liter Formulation

1. Sodium phosphate monobasic: 0.2 g

2. Sodium phosphate dibasic.7H₂O: 2.0 g

3. Sodium azide: 0.1 g

4. Sodium chloride: 9.4 g

5. q.s. to 1 liter with distilled water: pH approximately 7.4;osmolality 315 to 345 mOsm/kg.

Lymphocyte Hypotonic Solution

1. Sodium phosphate monobasic: 0.2 g

2. Sodium phosphate dibasic.7H₂O: 2.0 g

3. q.s. to 1 liter with distilled water: pH approximately 7.8;osmolality 15 to 25 mOsm/kg.

Procedure

1. Select avian red blood cells having a mean cell volume range of about140 to 170 fL. Wash the packed avian red blood cells with the phosphatebuffered saline solution (PBS).

2. Add 1.0 to 5.0 milligrams of cholesterol to a cell count of 2×10⁶ permicroliter and incubate for 2 to 6 hours, at room temperature.

3. Prepare a glutaraldehyde fixative reagent having a glutaraldehydecontent of about 0.1 to 0.8% by adding a commercial 25% glutaraldehydeproduct to the chilled Lymphocyte Hypotonic Solution. Preferably, thetemperature is from 20 to 8° C. The preferred concentration ofglutaraldehyde is approximately 0.35%.

4. Add the washed red blood cells to a measured amount of the fixativeof step 3 at a 1:35 dilution. Transfer to sealed containers which arerolled slowly for 18 to 24 hours at 2° to 8° C. The reduction inhemoglobin content is calculated to be approximately 60% by weight.

5. Remove the supernatant fluid, wash cells several times with the PBS,then resuspend in a suitable storing solution.

6. For a stand alone lymphocyte analog, resuspend the washed fixed cellsin the suspension media of this invention and adjust the concentrationto simulate that of human lymphocyte cells in normal human blood.

7. For multiple hematological parameters for a control product, add thewashed fixed cells in the suspension media of this invention with otherhematological compositions and analogs desired for the multipleparameter hematology control product, the cell count being appropriateto measure lymphocyte proportions.

8. With suitable stabilizers, the fixed cells can be stored for a timeperiod in excess of six months.

In accordance with the above example, but starting with other types ofmammalian red blood cells, comparable results are obtained.

EXAMPLE 2 Monocyte Cell Analog from Alligator Red Blood Cells

The following is a specific example of preferred reagents andrecommended specific procedural steps for treating alligator red bloodcells to obtain the monocyte cell analog. It will be understood that theformulations and the procedures are only illustrative and that otheringredients, proportions and procedures may be employed, in accordancewith the disclosures in this invention.

Monocyte Hypotonic Solution

1. Sodium phosphate monobasic: 0.1 g

2. Sodium phosphate dibasic 1.0 g

3. q.s. to 1 liter with distilled water; pH approximately 7.8;osmolality 5 to 15 mOsm/kg.

Washing solution for cells (PBS), as set forth in Example 1.

Procedure

1. Select alligator red blood cells having a mean cell volume range ofabout 350 to 450 fL. Wash the packed alligator red blood cells with PBS.

2. Add 1.0 to 5.0 milligrams of cholesterol to a cell count of 1×10⁶ permicroliter and incubate 3 to 5 hours at room temperature.

3. Prepare a glutaraldehyde fixing reagent having a glutaraldehydecontent of about 0.1 to 0.8% by adding a commercial 25% glutaraldehydeproduct to the chilled Monocyte Hypotonic Solution. Preferably thetemperature is from 2° to 8° C. The preferred concentration ofglutaraldehyde is approximately 0.15%.

4. Add the washed red blood cells to a measured amount of the fixativeof step 3 at a 1:50 dilution. Transfer to sealed containers which arerolled slowly for 18 to 24 hours at room temperature. The reduction inhemoglobin content is calculated to be approximately 40% by weight.

5. Remove the supernatant fluid, wash cells several times with the PBS,then resuspend in a suitable storing solution.

6. For a stand alone monocyte analog, resuspend the washed fixed cellsin the suspension media of this invention and adjust the concentrationto simulate that of human monocyte cells in normal human blood.

7. For multiple hematological control product, add the washed fixedcells in the suspension media of this invention with other hematologicalcompositions and analogs desired for the multiple parameter controlproduct in the appropriate concentration to measure monocyte cells.

8. With suitable stabilizers, the fixed cells can be stored for a timeperiod in excess of six months.

EXAMPLE 3 Eosinophil Analog from Red Blood Cells of the Alligator

The following is a specific example of preferred reagents andrecommended specific procedural steps for treating red blood cells ofthe alligator to obtain the eosinophil analog. It will be understoodthat the formulations and the procedures are only illustrative, and thatother ingredients, proportions and procedures may be employed, inaccordance with the disclosures in this invention.

Eosinophil Hypotonic Solution

1. Sodium phosphate monobasic: 0.32 grams

2. Sodium phosphate dibasic 8.08 grams

3. q.s. to 1 liter with distilled water; pH approximately 8.0;osmolality 75 to 85 mOsm/kg.

Eosinophil Hemoglobin Denaturing Treatment Solution

1. dimethyldicocoammonium chloride 2.5 grams

2. tris(hydroxymethyl)amino methane 6.06 grams (organic buffer)

3. q.s. to 1 liter with distilled water: pH approximately 10.5.

Eosinophil Post-Treatment Wash Solution

1. polyoxethylated alkylphenol 5 grams (Diazopan® SS-837 by GAF ChemicalCorp.)

2. q.s. to 1 liter with distilled water

Washing solution for cells (PBS), as set forth in Example 1.

Procedure

1. Select alligator red blood cells having a mean cell volume range ofabout 400 to 500 fL. Wash the packed alligator red blood cells with PBS.

2. Add 0.25 to 1.25 milligrams of cholesterol to a cell count of 1×10⁶per microliter and incubate 2 to 5 hours, at room temperature.

3. Prepare a glutaraldehyde cross linking reagent having aglutaraldehyde content of about 0.1 to 0.8% by adding a commercial 25%glutaraldehyde product to the Eosinophil Hypotonic Solution. Thepreferred concentration of glutaraldehyde is approximately 0.2%.

4. Add the washed red blood cells to a measured amount of the crosslinking of step 3 at a 1:50 dilution. Transfer to sealed containerswhich are rolled slowly for 18 to 24 hours at room temperature.

5. Remove the supernatant fluid, wash cells several times with the PBS.

6. Add the washed red blood cells to the Eosinophil HemoglobinDenaturing Treatment Solution at a 1:10 dilution. Transfer to sealedcontainers which are rolled slowly for 2-4 hours at room temperature.

7. Remove the supernatant fluid, wash cells several times with theEosinophil Post-Treatment Wash Solution to remove the EosinophilHemoglobin Denaturing Treatment Solution. Then resuspend in a suitablestorage solution.

8. For a stand alone eosinophil analog, resuspend the washed fixed cellsin the suspension media of this invention and adjust the concentrationto simulate that of human eosinophil cells in normal human blood.

9. For multiple hematological control products, add the washed fixedcells in the suspension media of this invention with other hematologicalcompositions and analogs desired for the multiple parameter controlproduct in the appropriate concentration to measure eosinophil cells.

10. With suitable stabilizers, the fixed cells can be stored for a timein excess of six months.

EXAMPLE 4 Neutrophil Cell Analog from Alligator Red Blood Cells

The following is a specific example of preferred reagents andrecommended specific procedural steps for treating alligator red bloodcells to obtain the monocyte cell analog. It will be understood that theformulations and the procedures are only illustrative and that otheringredients, proportions and procedures may be employed, in accordancewith the disclosures in this invention.

Neutrophil Hypotonic Solution

1. Sodium phosphate monobasic: 0.23 g

2. Sodium phosphate dibasic 5.32 g

3. q.s. to 1 liter with distilled water; pH approximately 8.0;osmolality 45 to 65 mOsm/kg.

Washing solution for cells (PBS), as set forth in Example 1.

Procedure

1. Select alligator red blood cells having a mean cell volume range ofabout 400 to 500 fL. Wash the packed alligator red blood cells with PBS.

2. Prepare a glutaraldehyde fixing reagent having a glutaraldehydecontent of about 0.1 to 0.8% by adding a commercial 25% glutaraldehydeproduct to the Neutrophil Hypotonic Solution. The preferredconcentration of glutaraldehyde is approximately 0.4%.

3. Add the washed red blood cells at a count of 1×10⁶ to a measuredamount of the fixative of step 3 at a 1:50 dilution. Transfer to sealedcontainers which are rolled slowly for 18 to 24 hours at roomtemperature.

4. Remove the supernatant fluid, wash cells several times with the PBS,then resuspend in a suitable storing solution.

5. Add packed cells to a nonionic surfactant solution. Said solutiontends to standardize the volume of donor cells. The solution comprises0.5 grams of octylphenoxy polyethoxy ethanol having an HLB ofapproximately 13.5 (Triton® X-100 by Rohm and Haas Co.,) in 1 liter ofdistilled water.

6. Remove the supernatant fluid, wash cells several times with the PBS,then resuspend in a suitable storing solution.

7. For a stand alone neutrophil analog, resuspend the washed fixed cellsin the suspension media of this invention and adjust the concentrationto simulate that of human neutrophil cells in normal human blood.

8. For multiple hematological control product, add the washed fixedcells in the suspension media of this invention with other hematologicalcompositions and analogs desired for the multiple parameter controlproduct in the appropriate concentration to measure neutrophil cells.

9. With suitable stabilizers, the fixed cells can be stored for a timeperiod in excess of six months.

EXAMPLE 5 Five Subpopulations of Leukocyte Analogs from Human WhiteBlood Cells

1. Add whole blood to a Dextran (molecular weight 100,000 to 500,000)solution at a dilution of 1:10 and allow to settle by gravity means for1 to 3 hours.

2. Remove the supernatant, which includes the white blood cells,platelets and some residual red blood cells.

3. Centrifuge the product of step 2 at less than 300 RCF for about 10minutes. Aspirate the platelets leaving the button of white blood cells,residual red blood cells, and a small amount of plasma with which toresuspend the cells.

4. Add a suitable lytic agent, such as water, to lyse the red bloodcells from the white blood cells.

5. Centrifuge the product of step 4 and remove supernatant, leavingpacked white blood cells. Resuspend the packed white blood cells in anapproximately equal volume of saline solution.

6. Add white blood cells to a suitable isoosmotic fixative solution,such as 5% formaldehyde and 95% PBS (volume percent), in a 1:10 dilutionand transfer to sealed containers which are rolled slowly for 18-30hours at room temperature.

7. Add a glutaraldehyde fixative solution having approximately a 0.1%concentration of glutaraldehyde at a 1:1 dilution to the pool, andcontinue fixation for an additional 8-12 hours.

8. Remove the supernatant fluid, wash cells several times with the PBS,then resuspend in a suitable storing solution.

9. For stand alone five subpopulation leukocyte analogs assembly,resuspend the washed fixed cells in the suspension media of thisinvention and adjust the concentration to simulate that of humanleukocyte cells in normal human blood.

10. For multiple hematological control product, add the washed fixedcells in the suspension media of this invention with other hematologicalcompositions and analogs desired for the multiple parameter hematologycontrol product, the cell count being appropriate to measure leukocytesproportions.

11. With suitable stabilizers, the fixed cells can be stored for a timeperiod in excess of six months.

EXAMPLE 6

In a sub-assembly for simulating the targeted composition of white bloodcells in a normal human blood sample, the following quantities of theindividual components are employed:

STOCK SOLUTION 0.150 L Example 1 lymphocytes 500 × 10³/uL 0.040 LExample 2 monocytes 500 × 10³/uL 0.030 L Example 3 eosinophils 500 ×10³/uL 0.280 L Example 4 neutrophils 500 × 10³/uL 0.500 L diluentphosphate buffered saline

In the final assembly of the four leukocyte populations, remove thesupernatant fluid, then resuspend the cells in 1.0 liter of an aqueoussolution of Moducyte® having a final concentration of 800 milligrams ofcholesterol.

This assembly can be stored for up to about six months with the additionof known suitable stabilizers.

The ratio and total cell count for the leukocyte populations can beadjusted to represent pathological, as well as normal conditions inhuman blood. These compositions are useful likewise in control andcalibrator products particularly for automated particle analysisinstruments employing the Coulter Principle. In addition, latexparticles can be added to the control product to provide a singlecontrol product that can further indicate instrument performance.

Suspensions of untreated human red blood cells, simulated white bloodcells, and stabilized or simulated platelets can be thereafter added insuch proportion that the final red blood cell, white blood cell andplatelet counts, as well as hemoglobin content and hematocrit fall inthe desired range.

Stabilized platelets are furnished by processes known in the art. Usefulprocesses include:

1. A combination of iodoacetamide and an iminodiacetic acid or saltthereof, together with a compatible bacteriostatic agent in an aqueoussolution which is maintained at a preselected range of pH and osmolalityas is described in U.S. Pat. No. 4,405,719.

2. A fixative-stabilizing composition containing a glutaraldehydeconcentration of 0.1% to 5% and a non-ionic surfactant which is amixture of ethoxylates of certain isomeric linear alcohols, as is morefully described in U.S. Pat. No. 4,389,490.

3. A human platelet analog comprising goat erythrocytes stabilized,combined and blended as necessary to have a size range and volumedistribution close to that of human platelets, as is described in U.S.Pat. No. 4,264,470.

The values for each of the hematological parameters can be varied torepresent abnormal low and abnormal high conditions. The white bloodcell count in normal blood is 5,000 to 11,000 per microliter (uL) with alymphocyte value of 20 to 40%, mononuclear cell value of less than 10%,a granulocyte value of 60 to 80%, eosinophil value less thanapproximately 5%, and basophil value less than approximately 2%. Thenormal range in human blood for red blood cells is 4,000,000 to5,000,000 cells per microliter. The normal hemoglobin value is 12 to 16grams/100 ml. The term “hematocrit” is defined as the ratio of volume ofpacked red blood cells to the volume of whole blood. The normal ratio inhumans is about 45%. The mean corpuscular volume is the ratio of thevolume of packed red blood cells in ml per liter of blood to red bloodcells in millions per microliter. The mean corpuscular hemoglobinconcentration is an index indicating the mean or average weight ofhemoglobin per 100 ml of packed red blood cells in terms of percent. Themean corpuscular hemoglobin is the ratio of hemoglobin content, in gramsper liter, to red blood cells, in millions per microliter.

While in the foregoing specification, a detailed description of theinvention has been set down for the purpose of illustration, manyvariations in the details herein give may be made by those skilled inthe art without departing from the spirit and scope of the invention.

We claim:
 1. A method for using a hematology control product todetermine an instrument malfunction cause comprising: a. placing ahematology control product in an instrument which differentiates atleast four populations of leukocytes based on electrical and opticalparameters, said control product containing at least one leukocyteanalog which has been derived from a blood cell which has been treatedso that it is resistant to degradation by the lytic reagents used inhematological test procedures; b. analyzing said hematological controlproduct in the instrument to obtain at least two values selected from DCMEAN, DC standard deviation, RLS MEAN, RLS standard deviation, opacitymean, opacity standard deviation, and COUNT RATIO, PEAK TO VALLEY RATIO,WHITE TIME and DATE TIME and combinations thereof; and c. determining acause of a malfunction of said instrument from said values of saidmeasured parameter.
 2. The method of claim 1, wherein said controlproduct comprises a neutrophil cell analog.
 3. The method of claim 1,wherein said control product further comprises lysable red blood cells.4. The method of claim 3, wherein said malfunction of the instrument isselected from the group consisting of instrument gain, debris and noise,instrument pump volume and instrument laser alignment and combinationsthereof.
 5. The method of claim 4 wherein said instrument reagent pumpvolume comprises lytic reagent pump volume.
 6. The method of claim 4wherein the instrument laser alignment comprises X axes alignment. 7.The method of claim 2 wherein the hematology control product comprisesat least a neutrophil analog and a lymphocyte analog.
 8. The method ofclaim 1, wherein the control product comprises at least three differentwhite blood cell analogs.
 9. The method of claim 8 wherein thehematology control product further comprises an aqueous solution of aplasma substance.
 10. The method of claim 9, wherein said plasmasubstance is selected from the group consisting of cholesterol,cholesterol esters, lipoprotein cholesterol, lipoprotein cholesterolesters, cholesterol combined with phospholipids, cholesterol combinedwith albumin, cholesterol esters combined with albumin, lipoproteincholesterol combined with phospholipids, lipoprotein cholesterolcombined with albumin and mixtures thereof.
 11. The method of claim 1wherein at least two measured parameter are used and one of the measuredparameters is DC MEAN of a leukocyte population.
 12. A method ofinstrument quality control for an instrument which differentiates atleast four populations of leukocytes comprising: a. analyzing at leastone leukocyte subpopulation in a quantity of normal patient bloodsamples in an instrument which differentiates at least four populationsof leukocytes based on electrical and optical parameters, to obtain astatistically significant value of at least two measured parameters; andsaid measured parameters are selected from DC MEAN, DC standarddeviation, RLS MEAN, RLS standard deviation, opacity mean, opacitystandard deviation, and COUNT RATIO, PEAK TO VALLEY RATIO, WHITE TIMEand DATE TIME and combinations thereof; and b. determining a malfunctionof said intrusment from said at least two values of said measuredparameters.
 13. The method of claim 12 wherein the malfunction of saidinstrument is selected from at least one member the group consisting oflysis debris and noise, instrument reagent pump volume setting,instrument laser alignment, instrument gain setting, flow rateinconsistency and combinations thereof.
 14. The method of claim 13wherein, said instrument reagent pump volume comprises lytic reagentpump volume.
 15. The method of claim 13 wherein the instrument laser